1. Field of the Invention
The present invention relates generally to methods and apparatus for testing integrated circuits, and more particularly to advanced probe cards and methods of fabricating the same.
2. Description of the Background Art
Probe cards are used in the testing of integrated circuits (ICs) by providing an interface between the pads of a bare die or chip formed on a wafer or substrate and test equipment.
One conventional type of probe card uses a large number of cantilevered arms extending obliquely outwardly from the planar surface of a substrate or a printed circuit board (PCB). Probe pins having needle-like tips extend from distal ends of the cantilevered arms to provide electrical contact with the pads on the die. The probe pins or the tips are typically made of a hard material, such as tungsten, to extend the operating life of the probe card. When the wafer is raised beyond the point at which the first pads on the die first come into contact with these tips, the arms flex so as to allow remaining tips on other arms to contact pads on the die, thereby compensating for any small variations in planarity or parallelism between the probe card and die or chip on the surface of the wafer. In addition, movement of the wafer past the point at which the tips contact pads on the die and the resultant flexing of the cantilever arms cause the tips to scrub across their respective pads thereby removing oxide buildup on the pads, and improving electrical contact between the probe card and the die.
One disadvantage of the above conventional approach is that the hardness of the tips of the probe pins and the typically limited movement of the cantilever arms can compensate for only small variations in planarity or parallelism between the surface of the die and the probe card. Moreover, even under ideal circumstances, the wafer typically receives some damage from the probe tip touch down. Thus, if the probe card is pushed against the wafer with a greater than usual force, such as to compensate for non-planarity or lack of parallelism, there is substantial likelihood that the wafer will be destroyed.
Another commonly used type of conventional probe card uses micro spring probes eliminating the need for cantilevered arms, and reducing if not eliminating damage to the wafer from solid tungsten probe pins. However, most spring probes have inherent limitations, such as limited pitch and limited pin count due to the size of the springs. More fundamentally, micro-spring probe cards have a substantially higher cost of fabrication than conventional cantilever probe cards.
Other additional disadvantages of both types of conventional probe cards include high cost, since a new or reconfigured probe card must be produced for each new IC layout, and long lead times required to produce a new or reconfigured probe card resulting in delays in chip production. This last problem arises because the layout or configuration of the probe card generally cannot be determined until the final mask for the IC is produced. Thus, availability of a probe card to test an IC can lag the initial production of the IC by four weeks or more.
Accordingly, there is a need for a probe card and a method using the same that are capable of compensating for significant variations in planarity or parallelism between the wafer and the probe card, without increasing the possibility of damage to the wafer. It is desirable that the probe card has a low cost relative to conventional advanced or high pin count probe cards. It is further desirable that new probe cards having a new configuration can be manufactured quickly, to reduce if not eliminate impact on chip production.